Silva Fennica vol. 54 no. 5 | 2020

• Sjølie, Inland Norway University of Applied Sciences, Postboks 400, 2418 Elverum, Norway E-mail: hanne.sjolie@inn.no

New mortality models were developed for the purpose of improving long-term growth and yield simulations in Finland, Norway, and Sweden and were based on permanent national forest inventory plots from Sweden and Norway. Mortality was modelled in two steps. The first model predicts the probability of survival, while the second model predicts the proportion of basal area in surviving trees for plots where mortality has occurred. In both models, the logistic function was used. The models incorporate the variation in prediction period length and in plot size. Validation of both models indicated unbiased mortality rates with respect to various stand characteristics such as stand density, average tree diameter, stand age, and the proportion of different tree species, Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and broadleaves. When testing against an independent dataset of unmanaged spruce-dominated stands in Finland, the models provided unbiased prediction with respect to stand age.

• Siipilehto, Natural Resources Institute Finland (Luke), Natural resources, P.O. Box 2, FI-00790 Helsinki, Finland E-mail: jouni.siipilehto@luke.fi
• Allen, Norwegian Institute of Bioeconomy Research (NIBIO), Division of Forest and Forest Products, NO-1431 Ås, Norway; Larson and McGowin Inc., Mobile, AL 36607, USA https://orcid.org/0000-0002-7824-2849 E-mail: micky.allen@nibio.no
• Nilsson, Swedish University of Agricultural Sciences (SLU), Southern Swedish Forest Research Centre, SE-23053 Alnarp, Sweden https://orcid.org/0000-0002-7624-4031 E-mail: urban.nilsson@slu.se
• Brunner, Norwegian University of Life Sciences (NMBU), Faculty of Environmental Sciences and Natural Resource Management, NO-1432 Ås, Norway https://orcid.org/0000-0003-1668-9714 E-mail: andreas.brunner@nmbu.no
• Huuskonen, Natural Resources Institute Finland (Luke), Natural resources, P.O. Box 2, FI-00790 Helsinki, Finland https://orcid.org/0000-0001-8630-3982 E-mail: saija.huuskonen@luke.fi
• Haikarainen, Natural Resources Institute Finland (Luke), Natural resources, P.O. Box 2, FI-00790 Helsinki, Finland https://orcid.org/0000-0001-8703-3689 E-mail: soili.haikarainen@luke.fi
• Subramanian, Swedish University of Agricultural Sciences (SLU), Southern Swedish Forest Research Centre, SE-23053 Alnarp, Sweden https://orcid.org/0000-0003-2777-3241 E-mail: narayanan.subramanian@slu.se
• Antón-Fernández, Norwegian Institute of Bioeconomy Research (NIBIO), Division of Forest and Forest Products, NO-1431 Ås, Norway https://orcid.org/0000-0001-5545-3320 E-mail: clara.anton.fernandez@nibio.no
• Holmström, Swedish University of Agricultural Sciences (SLU), Southern Swedish Forest Research Centre, SE-23053 Alnarp, Sweden https://orcid.org/0000-0003-2025-1942 E-mail: emma.holmstrom@slu.se
• Andreassen, Norwegian Institute of Bioeconomy Research (NIBIO), Division of Forest and Forest Products, NO-1431 Ås, Norway https://orcid.org/0000-0003-4272-3744 E-mail: kjellandreassen@gmail.com
• Hynynen, Natural Resources Institute Finland (Luke), Natural resources, P.O. Box 2, FI-00790 Helsinki, Finland E-mail: jari.hynynen@luke.fi

Vaccinium myrtillus L., V. vitis-idaea L. and V. uliginosum L. belong to the genus Vaccinium. These wild species are widely distributed and ecologically important within the Baltic countries but they have not been extensively studied using molecular markers. EST-SSR and cpSSR markers were used to investigate the population structure and genetic diversity of these species to obtain information useful for the development of in situ conservation strategies. Wild Vaccinium species populations are moderately genetically differentiated, with some populations more highly differentiated, but without higher order clustering of groups of populations, indicating that there are no dispersal barriers for these species within the Baltic countries. Genetic diversity of populations growing in protected areas, managed forests and intensively utilised public recreational areas is similar. The results from this study can be utilised for the selection of populations for the in situ conservation of the studied Vaccinium species. In addition, complementary ex situ conservation strategies can be used for the preservation of rare varieties (e.g. V. myrtillus var. leucocarpum).

• Gailīte, Genetic Resource Centre, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, Salaspils, Latvia, LV-2169 E-mail: agnese.gailite@silava.lv
• Gaile, Genetic Resource Centre, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, Salaspils, Latvia, LV-2169 E-mail: anita.gaile@silava.lv
• Ruņģis, Genetic Resource Centre, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, Salaspils, Latvia, LV-2169 https://orcid.org/0000-0001-5173-2912 E-mail: dainis.rungis@silava.lv

Expertise in the cost-efficient utilization and treatment of brushwood on forest roadside sites is limited. In the present study, the productivity of brushwood clearing and harvesting on forest roadside sites was defined by creating time-consumption models or parameters for the aforementioned working methods. Compiled time consumption models and parameters for the brushwood clearing and harvesting can be used as a basis for evaluating alternative management practices and to determine when brushwood biomass should be harvested and when it should be left to decay. The harvesting of brushwood was based on the harwarder system and the clearing of brushwood was done with a spiral cutter, which is a novel accessory for cutting roadside vegetation. Based on the study results, the average volume of harvested brushwood and forwarding distance are the key elements that have an effect on harvesting productivity with harwarders. Correspondingly, stump diameter has a strong impact on the clearing productivity of brushwood. The plot-wise productivity of the spiral cutter in brushwood clearings varied in the range of 0.19–0.61 ha per PMh. An increase in stump diameter slowed down the clearing productivity of the spiral cutter and there was a clear step downward in clearing productivity as the average diameter increased from 30 mm to 40 mm. The machinery under study operated well and there were no interruptions due to machine breakdowns.

• Laitila, Natural Resources Institute Finland (Luke), Production systems, P.O. Box 68, FI-80101 Joensuu, Finland E-mail: juha.laitila@luke.fi
• Väätäinen, Natural Resources Institute Finland (Luke), Production systems, P.O. Box 68, FI-80101 Joensuu, Finland E-mail: kari.vaatainen@luke.fi

In Nordic forests, consistent evidence about better seedling survival rate and increased growth due to site preparation have been obtained in numerous studies. Proper site preparation method can reduce costs of the whole regeneration chain through its effects on survival of planted seedlings, abundance of natural regeneration and competition in early stand development. This study compared the natural regeneration of birches (silver birch (Betula pendula Roth) and downy birch (B. pubescens Ehrh.)), amount of exposed mineral soil, and growth of planted seedlings between spot mounding and inverting site preparation methods. Present study was conducted in eight forest stands established in 2012 or 2015. Even though difference was not statistically significant, inverting exposed less mineral soil than spot mounding and thus reduced the natural regeneration of birch seedlings by 6135 seedlings ha^–1 compared to spot mounding. However, the variation between regeneration areas was remarkable. There was no difference in seedling mortality or growth between the site preparation methods. In order to achieve high growth of conifers, moderate amount of exposed mineral soil and thus less naturally regenerated birch, inverting should be favored over spot mounding.

• Laine, Metsä Group, P.O. Box 208, FI-70101 Kuopio, Finland E-mail: tiina.laine@metsagroup.com
• Kankaanhuhta, Natural Resources Institute Finland (Luke), Natural resources, Juntintie 154, FI-77600 Suonenjoki, Finland E-mail: ville.kankaanhuhta@luke.fi
• Rantala, Metsä Group, P.O. Box 10, FI-02020 METSÄ, Finland E-mail: juho.rantala@metsagroup.com
• Saksa, Natural Resources Institute Finland (Luke), Natural resources, Juntintie 154, FI-77600 Suonenjoki, Finland E-mail: timo.saksa@luke.fi

The diameter at any point on a stem and tree volume are some of the most important types of information used in forest management planning. One of the methods to predict the diameter at any point on a stem is to develop taper models. Black locust (Robinia pseudoacacia L.) occurs in almost all forests in Poland, with the largest concentration in the western part of the country. Using empirical data obtained from 13 black locust stands (48 felled trees), seven taper models with different numbers of estimated parameters were analysed for section diameters both over and under bark using fixed and mixed-effects modelling approaches. Assuming a lack of additional measurements, the best fitted taper models were used for the prediction of over bark volume using both methods. The predicted volume was compared with the results from different volume equations available for black locust. The variable-form taper model with eight estimated parameters fitted the data the best. The lowest root mean square error for volume prediction was achieved for the elaborated fixed-effects taper model (0.0476), followed by the mixed-effects taper model (0.0489). At the same time, the difference between the volume relative errors achieved based on the taper models does not differ significantly from the results obtained using the volume equations already available for black locust (two of the three analysed).

• Bronisz, Institute of Forest Sciences, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, PL 02-776 Warsaw, Poland E-mail: karol.bronisz@wl.sggw.pl
• Zasada, Institute of Forest Sciences, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, PL 02-776 Warsaw, Poland https://orcid.org/0000-0002-4881-296X E-mail: Michal.Zasada@wl.sggw.pl

Fire is a common disturbance in boreal forests causing changes in biological diversity at various spatial scales. In the past 100 years, forest management has limited fire outbreaks, but in the future, the fire-affected forest area is expected to increase in many regions due to climate change. Burned forests are typically salvage-logged, but the effect of this type of management versus natural regeneration on biological diversity is not well understood, particularly the mid-term effect to tree establishment and understory vegetation composition and diversity. Various management methods were used after a large fire in 1992 in a peatland-forest complex and neighbouring managed forests, which created an experimental setup for study of the effect of management after fire in the Sliteres National park, northwestern Latvia. Understory vegetation was described in plots using a design of four forest and three management types: natural regeneration (unmanaged) and managed sites with salvage logging followed by no further human intervention and salvage logging with planting. Post-fire management had different effect in each forest type. Species richness was higher in forest types with salvage logging than in natural regenerated sites on rich wet and rich dry forest types, but not for the poor forest types. Tree regeneration was generally greater in salvage-logged stands, but differed between forest types. Species composition was related to tree regeneration and canopy openness. In contrast to other studies, salvage logging had a positive mid-term effect to ground vegetation diversity and tree establishment in the studied stands, implying potential for concomitant management and conservation of ground cover vegetation in semi-natural stands.

• Kārkliņa, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, LV-2169, Salaspils, Latvia E-mail: annija.karklina@silava.lv
• Brūmelis, University of Latvia, Faculty of Biology, Jelgavas street 1, LV-1004, Riga, Latvia E-mail: guntis.brumelis@lu.lv
• Dauškane, University of Latvia, Faculty of Biology, Jelgavas street 1, LV-1004, Riga, Latvia E-mail: iluta.dauskane@lu.lv
• Elferts, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, LV-2169, Salaspils, Latvia; University of Latvia, Faculty of Biology, Jelgavas street 1, LV-1004, Riga, Latvia E-mail: didzis.elferts@lu.lv
• Freimane, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, LV-2169, Salaspils, Latvia E-mail: lasma.freimane@silava.lv
• Kitenberga, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, LV-2169, Salaspils, Latvia E-mail: mara.kitenberga@silava.lv
• Lībiete, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, LV-2169, Salaspils, Latvia E-mail: zane.libiete@silava.lv
• Matisons, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, LV-2169, Salaspils, Latvia E-mail: robism@inbox.lv
• Jansons, Latvian State Forest Research Institute “Silava”, 111 Rigas Street, LV-2169, Salaspils, Latvia E-mail: aris.jansons@silava.lv

The purpose of this study was to prepare a comprehensive, computerized teak (Tectona grandis L.f) plantation yield model system that can be used to describe the forest dynamics, predict growth and yield and support forest planning and decision-making. Extensive individual tree and permanent sample plot data were used to develop tree-level volume models, taper curve models and stand-level yield models for teak plantations in Panama. Tree volume models were satisfactorily validated against independent measurement data and other published models. Tree height as input parameter improved the stem volume model marginally. Stand level yield models produced comparable harvest volumes with models published in the literature. Stand level volume product outputs were found like actual harvests with an exception that the models marginally underestimate the share of logs in very large diameter classes. The kind of comprehensive model developed in this study and implemented in an easy to use software package provides a very powerful decision support tool. Optimal forest management regimes can be found by simulating different planting densities, thinning regimes and final harvest ages. Forest practitioners can apply growth and yield models in the appropriate stand level inventory data and perform long term harvest scheduling at property level or even at an entire timberland portfolio level. Harvest schedules can be optimized using the applicable financial parameters (silviculture costs, harvesting costs, wood prices and discount rates) and constraints (market size and operational capacity).

• Seppänen, Verdas Oy, Kihlinkuja 7, FI-50600 Mikkeli, Finland E-mail: petteri@verdas.fi
• Mäkinen,  Simosol Oy. Hämeenkatu 10, FI-11100 Riihimäki, Finland E-mail: antti.makinen@simosol.fi

In remote sensing-based forest inventories 3D point cloud data, such as acquired from airborne laser scanning, are well suited for estimating the volume of growing stock and stand height, but tree species recognition often requires additional optical imagery. A combination of 3D data and optical imagery can be acquired based on aerial imaging only, by using stereo photogrammetric 3D canopy modeling. The use of aerial imagery is well suited for large-area forest inventories, due to low costs, good area coverage and temporally rapid cycle of data acquisition. Stereo-photogrammetric canopy modeling can also be applied to previously acquired imagery, such as for aerial ortho-mosaic production, assuming that the imagery has sufficient stereo overlap. In this study we compared two stereo-photogrammetric canopy models combined with contemporary satellite imagery in forest inventory. One canopy model was based on standard archived imagery acquired primarily for ortho-mosaic production, and another was based on aerial imagery whose acquisition parameters were better oriented for stereo-photogrammetric canopy modeling, including higher imaging resolution and greater stereo-coverage. Aerial and satellite data were tested in the estimation of growing stock volume, volumes of main tree species, basal area and diameter and height. Despite the better quality of the latter canopy model, the difference of the accuracy of the forest estimates based on the two different data sets was relatively small for most variables (differences in RMSEs were 0–20%, depending on variable). However, the estimates based on stereo-photogrammetrically oriented aerial data retained better the original variation of the forest variables present in the study area.

• Tuominen, Natural Resources Institute Finland (Luke), Bioeconomy and Environment, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: sakari.tuominen@luke.fi
• Balazs, Natural Resources Institute Finland (Luke), Bioeconomy and Environment, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: andras.balazs@luke.fi
• Kangas, Natural Resources Institute Finland (Luke), Bioeconomy and Environment, P.O. Box 68, FI-80101 Joensuu, Finland E-mail: annika.kangas@luke.fi

Forest inventories assisted by wall-to-wall airborne laser scanning (ALS), have become common practice in many countries. One major cost component in these inventories is the measurement of field sample plots used for constructing models relating biophysical forest attributes to metrics derived from ALS data. In areas where ALS-assisted forest inventories are planned, and in which the previous inventories were performed with the same method, reusing previously acquired field data can potentially reduce costs, either by (1) temporally transferring previously constructed models or (2) projecting field reference data using growth models that can serve as field reference data for model construction with up-to-date ALS data. In this study, we analyzed these two approaches of reusing field data acquired 15 years prior to the current ALS acquisition to estimate six up-to-date forest attributes (dominant tree height, mean tree height, stem number, stand basal area, volume, and aboveground biomass). Both approaches were evaluated within small stands with sizes of approximately 0.37 ha, assessing differences between estimates and ground reference values. The estimates were also compared to results from an up-to-date forest inventory relying on concurrent field- and ALS data. The results showed that even though the reuse of historical information has some potential and could be beneficial for forest inventories, systematic errors may appear prominent and need to be overcome to use it operationally. Our study showed systematic trends towards the overestimation of lower-range ground references and underestimation of the upper-range ground references.

• de Lera Garrido, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: ana.maria.lera.garrido@nmbu.no
• Gobakken, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: terje.gobakken@nmbu.no
• Ørka, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: hans-ole.orka@nmbu.no
• Næsset, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: erik.naesset@nmbu.no
• Bollandsås, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: ole.martin.bollandsas@nmbu.no

Trees are particularly susceptible to climate change due to their long lives and slow dispersal. However, trees can adjust the timing of their growing season in response to weather conditions without evolutionary change or long-distance migration. This makes understanding phenological cueing mechanisms a critical task to forecast climate change impacts on forests. Because of slow data accumulation, unconventional and repurposed information is valuable in the study of phenology. Here, I develop and use a framework to interpret what phenological patterns among provenances of a species in a common garden reveal about their leafing cues, and potential climate change responses. Species whose high elevation/latitude provenances leaf first likely have little chilling requirement, or for latitude gradients only, a critical photoperiod cue met relatively early in the season. Species with low latitude/elevation origins leafing first have stronger controls against premature leafing; I argue that these species are likely less phenologically flexible in responding to climate change. Among published studies, the low to high order is predominant among frost-sensitive ring-porous species. Narrow-xylemed species show nearly all possible patterns, sometimes with strong contrasts even within genera for both conifers and angiosperms. Some also show complex patterns, indicating multiple mechanisms at work, and a few are largely undifferentiated across broad latitude gradients, suggesting phenotypic plasticity to a warmer climate. These results provide valuable evidence on which temperate and boreal tree species are most likely to adjust in place to climate change, and provide a framework for interpreting historic or newly-planted common garden studies of phenology.

• Salk, Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, P.O. Box 49, SE- 230 53 Alnarp, Sweden; Faculty of International Studies, Utsunomiya University, 350 Minemachi, Utsunomiya-shi, Tochigi 321-8505 Japan; Institute for Globally Distributed Open Research and Education (IGDORE) E-mail: carl.salk@slu.se